Magnet structure



Nov. 7, 1961 L. c. KELSEY EFAL 3,008,052

MAGNET STRUCTURE Filed April 17, 1958 United States Patent 01 3,008,052 MAGNET STRUCTURE Lawrence C. Kelsey, Kenneth E. Grosse, and Eugene B. Szymczak, Chicago, Ill., assignors to W. M. Welch Mfg. Co., Chicago, Ill., a corporation of fllinois Filed Apr. 17, 1958, Ser. No. 728,957 Claims. (Cl. 250200) The present invention is directed to a new and improved form of magnet structure particularly adapted for use in modulating the discharge current of a photocell forming a part of a light-measuring system in which the photocell functions to emit electrons in response to the incidence of light.

In the modulation of a discharge current for amplification thereof into a readily measurable current, an electro-magnet is used to set up a field of magnetic flux directed between the electrodes of a photocell. An alternating or pulsating voltage is supplied by the magnet structure establishing the magnetic field with this voltage being applied to the electrodes of the photocell so that minute photo-electric current occurring in the photocell in response to the incidence of light is modulated at the frequency of the applied alternating or pulsating voltage. This results in an increase in the frequency of the photo electric current to provide the arrangement with greater sensitivity in connection with the ability of the system to detect smaller discharge currents of the photocell. The use of this type of an arrangement in a lightmeasuring device is fully disclosed in US. Patent No. 2,424,933.

In a magnetically modulated discharge vessel of the type described, as particularly disclosed in the aforementioned patent, it is considered important to reduce magnetic flux loss and maintain such loss at a minimum while concentrating the desired. modulating field in the area where greatest modulation effect can be obtained. In practice, modulating magnet structures have been used successfully at low frequencies, such as below 100 c.p.s., but upon attempting to increase the modulating frequency it has been found that eddy current losses in nearby metal portions, such as the casing of the device or supports therefor, become very substantial. The presence of ferrous materials near the magnet structure further increases the field losses and reduces the effective modulation of the discharge currents of the photocell by causing the magnetic flux line to deviate from their predetermined path. The existence of eddy currents in the form of deviating flux contributes to the pickup of unwanted signal potentials from the vicinity of the dis charge vessel and place a severe limitation on the achievement of higher sensitivities in the device.

In an effort to overcome the aforementioned problems, rather extreme steps have been taken to reduce fiux loss and extraneous effects on the magnetic field particularly in high sensitivity circuits. No adequate solution has been found and magnetic shielding or special positioning of the elements of the device in an effort to reduce the flux loss and extraneous effects on the magnetic field have not been found practical. Photocells must be maintained in an open field to perform the intended function of light-measurement and must be positioned between the pole pieces of the magnet for optimum modulation of the discharge current.

It is an object of the present invention to provide a new and improved magnet structure particularly adapted for use in modulating the discharge current of a discharge vessel such as a photocell, the structure including means for defining a concentrated magnetic field to at least substantially eliminate stray flux effects and losses for high sensitivity operation.

Still a further object is to provide a new and improved magnet structure capable of operation at increased modulating frequencies Without appreciable eddy current losses and without being adversely affected by close proximity to large metal masses, the structure including the use of a balanced assembly of coils wound in the manner of a bifilar transformer with the pole pieces thereof in spaced relation to receive therebetween a discharge vessel such as a photocell, the structure further including a magnetic field confining yoke arrangement surrounding the coils to provide a continuous path for magnetic flux to either side of the discharge vessel and at least substantially eliminate stray flux effects and losses.

Other objects not specifically set forth will become apparent from the following detailed description made in conjunction with the drawings wherein:

FIG. 1 is a perspective of the improved magnet structure of the present invention;

FIG. 2 is a vertical section in elevation of the structure; and

FIG. 3 is an end view of the structure illustrating schematically the controlled magnetic field of the same.

Referring particularly to FIGS. 1 and 2, a magnet structure 10 is illustrated as including a pair of spaced coils 1 1 and 12 received within a two-piece frame formed from top and bottom frame members 13 and 14, respectively. Each of the coils 11 and 12 are wound on core elements 15 which are tubular and which are provided with radial end face flanges 16 and 17.

The coils 11 and 12 are mounted in spaced relation within the frame members 13 and 14 with the inner, oppositely positioned end plate portions 16 thereof constituting pole pieces between which a photocell 18 (FIG. 2) is received. The windings 19 of each of the coils 11 and 12 are started at the outer ends thereof in association with the end plate portions 17 and are advanced toward the inner end plates or poles 16. In this respect, the coils 11 and 12 are wound in series with their fields mutually aiding. In eifect, the outside windings represent the electrical center of both coils in series and the inside windings represent the ends or terminals of the two coils in series with the resistance being the same for each coil. The electrical field is balanced and the terminal ends as defined by the end plates 17 are as far as possible from the photocell to eliminate stray electric pickup by the photocell.

The top and bottom frame members 13 and 14 are of identical construction, each being provided with a flat central portion which is centrally apertured to define oppositely positioned openings 20 aligned with the space between the pole pieces 16. Opposite end margins of each of the frame members 13 and 14 are flanged inwardly at 21 to enclose the outer ends of the coils 11 and 12. Integrally formed, reversely folded frame member attaching portions in the form of tongues 22 are located centrally of the inwardly positioned edges of the flanges 21 and are received within the cores 15 in clamping and supporting engagement therewith to fixedly position the coils 11 and 12 in the structure.

To complete the structure, a plurality of strip plates 23 are received between the opposed surfaces of the tongues 22- within the hollow centers of the cores 15. The plates 23 are stacked in the form of laminations of surficient thickness to tightly hold the tongues 22 within the cores and rigidify the structure. The frame members '13 and 14 and the strip plates 23' are formed from high permeability, magnetic material such as mu-metal which can be readily die-cut and formed into the shapes described. The frame members 13 and 14- are assembled with the coils 11 and 12 having the mounting tongues 22 received within the cores 15 and the plates 23 tightly inserted between the tongues 22 within the cores 15 to finish the overall assembly.

The structure described is of compact, inexpensive design while being capable of highly efiicient use in the modulation of the discharge current of a photocell. FIG. 3 schematically illustrates operation of the structure 10 with the coils 11 and 12 thereof being supplied by leads 24 with an alternating current from a suitable source such as included in the system disclosed in U.S'. Patent No. 2,424,933. The inner ends of the coils 11 and 12 have attached thereto leads 25 which are connected to a source such as an oscillator in line with the disclosure of the aforesaid patent.

The magnetic field of modulating frequency is established by the structure 10' as indicated by the flux lines 26 schematically shown in FIG. 3. The field is directed across the photocell 18 between the electrodes 27 and 28 thereof. The electrode 28- is arouate in shape and is arranged so that light can impinge thereon and so that electrons are emitted from the surface thereof when light does contact the same. This type of electrode is well known and is normally coated with electron-emissive material such as cesium or potassium. The electrodes 27 collect electrons emitted from the electrodes 28 as a result of light impingement.

The magnetic field 26 is directed between the electrodes 27 and 28 perpendicular to the axes thereof so that when the magnetic field is of sufficient intensity, electrons cannot pass from electrode 28 to electrode 27. The magnetic field deflects the electron stream to prevent collection thereof by the electrodes 27. During periods of reduced intensity of the magnetic field, the electron stream is collected by the electrodes 27 to an extent as controlled by the intensity of the magnetic field. The coils 11 and 12 are periodically energized so that the magnetic field between the electrodes 27 and 28 is alternating in intensity and is of just sufiicient intensity to prevent the passage of electrons between the electrodes 27 and 28 except during alternate intervals occurring at twice the frequency of the magnetic field. Thus, the alternating magnetic field between the electrodes modulates the output current of the photocell at a frequency which is twice that of the magnetic field and the output of the photocell may then conveniently be amplified through an electron discharge amplifier device included in the system as disclosed in the aforesaid patent.

As briefly described, the functioning of the magnet structure 10 in combination with the photocell 18 is entirely conventional, the essence of the present invention residing in the structural features of the device disclosed. The combined frame members 13 and 14 and plates 23 constitute a wrap-around yoke in which the magnetic field is concentrated to provide the most efiicient use of available flux. The magnetic field by reason of its concentration in the yoke structure is not affected in an adverse manner by close proximity to any large metal masses whether ferous or non-ferrous. As previously described, the use of spaced coils wound in the manner described prevent in combination with the yoke any substantial external radiation of flux from the structure. The flux is confined by the structure while retaining the open field arrangement readily adapted to receive therein the photocell. The openings Zfl in the frame members 13 and 14 assure efiicient operation of the photocell 18 in response to the incidence of light without interfering with magnetic field concentration.

One of the most important features of the improved structure of the present invention resides in the successful use of the same at increased modulating frequencies. As previously described, increased frequencies of above c.p.s. cause eddy current losses in surrounding metallic objects. Modulating frequencies may be materially increased without accompanying eddy current losses and while retaining a requisite sensitivity of the device. The frame members 13 and 14 of the magnet structure 10 not only confine the field established by the coils 11 and 12 but also function as a case for the structure containing all of the operative elements therein. The structural features described including the series windings of the coils cooperate to provide a balanced assembly suitable for use with a photo-tube for optimum modulation of the discharge current thereof.

Obviously certain modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In combination, a magnet structure, a discharge vessel received within said magnet structure, said magnet structure comprising spaced axially aligned coils wound in series and arranged to provide mutually aiding fields, pole pieces defining the innermost ends of said coils, said discharge vessel being positioned between said pole pieces, the outermost terminal ends of said coils being spaced from said discharge vessel to eliminate stray electrical pick-up thereby, and a pair of frame pieces cooperatively supporting said coils and extending along opposite surfaces of said magnet structure about said discharge vessel to substantially enclose said coils and form a flux path to at least substantially eliminate stray flux effects and losses, said frame pieces being apertured on opposite sides of said discharge vessel to facilitate operation of said vessel, each of said frame pieces being in the form of centrally apertured plates having inturned end margins encasing the terminal ends of said coils and provided with integrally formed reversely folded tongues of reduced width which are received in the cores of said coils.

2. The combination of claim vessel is a photocell.

3. In combination, a magnet structure, a discharge vessel received within said magnet structure, said magnet structure comprising spaced axially aligned coils wound in series and arranged to provide mutually aiding fields, pole pieces defining the innermost ends of said coils, said discharge vessel being positioned between said pole pieces, the outermost terminal ends of said coils being spaced from said discharge vessel to eliminate stray electrical pick-up thereby, a pair of frame pieces cooperatively supporting said coils and extending along opposite surfaces of said magnet structure about said discharge vessel to substantially enclose said coils and to form a flux path to at least substantially eliminate stray flux effects and losses, said frame pieces being apertured on opposite sides of side discharge vessel to facilitate operation of said vessel, each of said frame pieces being in the form of centrally apertured plates having inturned end margins encasing the terminal ends of said coils and provided with integrally formed reversely folded tongues of reduced width which are received in the cores of said coils, and flux path laminations in the form of strip plates filling the cores of said coils between said tongues received therein.

4. The combination of claim 3 wherein said discharge vessel is a photocell.

5. In combination, a magnet structure, a discharge 1 wherein said discharge vessel received within said magnet structure, said magnet structure comprising spaced axially aligned coils wound in series and arranged to provide mutually aiding fields, pole pieces defining the innermost ends of said coils, said discharge vessel being positioned between said pole pieces, the outermost terminal ends of said coils being spaced from said discharge vessel to eliminate stray electrical pick-up thereby, and a pair of frame pieces cooperatively supporting said coils and extending along opposite surfaces of said magnet structure about said discharge vessel to substantially enclose said coils and form a flux path to at least substantially eliminate stray flux effects and losses, each of said frame pieces being in the form of a flat plate having inturned marginal end portions cooperatively encasing the terminal ends of said coils and attached to the cores of said coils, at least one of said plates being centrally apertured to expose said discharge vessel.

References Cited in the file of this patent UNITED STATES PATENTS 

